Production of bulky colorspun rayon yarn



July 21, 1959 I HYUNGDUK YOO 2,895,288

I PRODUCTION 0F BULKY COLORSPUN RAYON YARN Filed Sept. 21, 1956 COLOR- SPUN RAYON SU PER 'TWISTING .(SPOOL) TREAT WITH HOT FORMALDEHYDE AND ACIDIC CATALYST GENTRIFUGING DRYING CURING (SPOOL) DETWISTING TO ZERO BULKY YARN United States Patent PRODUCTION "OF BULKY COLORSPUN RAYON .YARN

Hyungduk Yoo, Swarthmore, Pa, assignor to American Viscose Corporation, Philadelphia, Pa., a CGRPOl'fitlOIl of ljlaware v Application'September 21,- 1956, SerialNo. 611,217

6" Claims. (Cl. 57 -164) The present invention is directed toward a process for the preparation of bulky yarn. More specifically it' is directed to a process for making a laundry-resistant bulkyrayon yarn by treating yarn chemically along with mechanical twisting and de-twisting.

It is known in the prior art that thermoplastic yarns such as nylon may be given a fairly permanent crimp by. heating highly twisted yarn, preferably in the presence of steam, to set the twist, followed by untwisting. The resulting yarn has a strongly curled or crimped woolly appearance -(see U.S. 2,290,253 and 2,564,245). The prior art describes a process wherein a rayon yarn is impregnated withformaldehyde, twisted, cured, and detwisted to produce a woolly yarn. In a modification of this process a rayon yarn is given a supertwist, moistened. to set thetwist, untwisted to produce a wool-*likeyarn, and then treated with formaldehyde in the presence of an acidic catalyst followed by thermal curing. Both processes however require reacting the cel- Iulosic yarn; with formaldehyde under strongly acidic conditions which cause severe damage to the fiber structure through, depolymerization and hydrolysis of the cellulose, aswell as causing excessive cross-linking, with resulting embrittlement of the fiber and reduced extensibility.- In addition'such yarns are difficult to dye after this treatment dueto resinification of the surface. A process has been needed whichwill preserve the residual yarn properties of the fiber while at the same time eifecting the desired cross-linking.

Accordingly it is an object of the present invention to prepare a cross-linked cellulosicfiber by means which willavoid the degradation of the fiber which accompanies conventional methods of formaldehyde treatment. A further object is the provision of means for producing. a bulky cellulosic yarn which can be more rapidly crosslinked by conventional means than plain viscose rayon and will have a lower water retention and a correspondinglygreater dimensionalstability when wet- A further object is the provision of a process of the foregoing type which will avoid the dyeing difiiculties mentioned above.

These objects are achieved according to the present invention by supertwisting a color-spun (pigmented) rayon yarn; setting the twist therein by treating the supertwisted yarn with-hot liquid formaldehyde in the presenceof a mildly acidic catalyst, then drying and curing to effect cross-linkage between the formaldehyde and the cellulose, followedby detwisting. The general flow pattern is illustrated 'by the figure; The resulting yarn is very fluify and crimped due to retention of some of the twist and i't retains the twist when immersed in water. It is believed that the small pigment particles embedded in the yarn open up'the cellulosic structure, making it more accessible to the hot formaldehyde, and thus permit a considerably greater amount of surface reaction between thecellulose and formaldehyde than would be the case with anunpigmented rayon fiber. Hence, the color-spun yarn canbe' cross-linked withfor'maldehyde in shorter time than could a plain viscose rayon fiber, which means 2 a shorter time of exposure of the fiber to the acid reaction environment. This of course results in less fiber degradation as described above. This process also avoids the uneven dyeing which would result if the dye were applied to the cross-linked detwisted fiber.

Suitablecolored inorganic pigment may be employed to obtain the desired color or shade. For a yellow color, ochre, sienna, chrome yellow, tin bronze, etc., may be employed. For a red color Venetian red, red lead, vermillion, etc., may be employed. For a blue color, ultramarine, Prussian blue, Milori blue, etc., may be used. For green, Guignetsgreen Verdigris, chrome green may be employed. For brown, raw umber, burnt umber or Van'dyke brown may be used. Toob'ta'in metallic effects, finely divided or colloidal metals may beemployed. For shading, that is to get darker colors, lamp black, graphite or other'black pigment'may be added. To obtain any other colors, the pigments may be mixed'as is well understood in the paint art.

The pigment is preferably added to'the dope or spinning solution containing the cellulose compound in the form of a concentrated suspension in a liquid; usually about a 20% pigment-in-water dispersion. The amount of pigment added will vary with the depth of color desired and the nature of the pigment employed'and will generally be from 0.1 to 10% of the weight of the cellulosic material present in the finished yarn. The pigment is preferably in very fine form, the particles having a diameter of less than 0.1 to 5 microns for increased covering power. It is of importance to have the pigment of very fine size inorder to' obtain the desired depth of color without the necessity of incorporating a large amount of pigment as to'deleteriously affect the strength and the other properties of the yarn. This fine size may be-obtained by grinding the inorganic colored pigment either with water, an oil, part of the spinning solution, or the solvent used in the spinningsolution in a ball mill or colloid mill.

The viscose, the spinning bath, etc., used in spinning the regenerated cellulose film is no part of the present invention and will not be detailed here. In general the viscose used is a normal orplain viscose having a sodium chloride salt test'value of from 3 to 6, containing from 6 to-9% cellulose, from 6 to 9% sodium hydroxide and ofnormal spinning viscosity.

The setting bath-into which the modified viscose is extruded may be a coagulating and cellulose-regenerating bath of the composition normally used in the manufacture of fibers or yarns from viscose. Aqueous baths containing from 7 to 13.5% sulfuric acid and from 18 to 28% sodium sulfate are satisfactory. The bath may also containcomparatively small amounts, for example, from 0.1to-5 of zinc sulfate, as well as small amounts of other adjuvants or assistants. If it is desired toproduce self -crimpable fibers of the type described in U.S. 2,517,694 to Merion and Sisson, spinning baths as described in that patent may be used.

EXAMPLE I A .spinnable-viscosesolution was extruded through a 30 hole jet at the-rate of 60 n1./m. into an aqueous coagulating bath containing 9.2% sulfuric acid, 1.0% zinc sulfate, and 17% sodium sulfate. The bath temperature was 50 C. Into the viscose was continuously injected an aqueous dispersion of Cardinal Red pigment formulated as injected from 16% Red 4RHVS0.5% Blue BVS, these percentages expressed as weight of pigment dispersion based on cellulose. The Blue BVS is a 22% dispersion of a phthalocyanine type material. The Red 4RHVS is a 15% dispersion of an azo pigment The coagulated filaments were drawn from the spinning bath in the form of a multifilament yarn, stretched 30% between godets, and collected as a cake by box-spinning.

The cake is dofied, wet-processed by conventional means, i.e., washed acid-free, desulfided, water rinsed, bleached, and treated successively with acid, antichlor, water, and a soft finish, followed by drying.

A skein of the finished yarn of 300 denier and 30 filaments was then given a twist of 45 t.p.i. (turns per inch) and wound on a spool under tension. In this form it was soaked for 20 minutes at 84 C. in a water solution of formaldehyde, 3.6% methanol, and 0.3% of a catalyst comprising the reaction product of 1.0 mole HCl, 0.9 mole monoethanolamine, and 2.0 moles formaldehyde (percentages are by weight based on total solution). The pH of the soaking bath was 3.5. The impregnated yarn was centrifuged to remove excess liquid, then dried for 25 minutes at 75 C., cured for 35 minutes at 150 C., and detwisted 47 t.p.i. The resulting yarn is strongly crimped and wool-like, and this eifect is substantially fast to Washing. In addition, its swelling capacity in water is reduced compared to that of plain viscose yarn.

EXAMPLE II Another skein of the same yarn used in Example I was treated as in Example I but the curing catalyst was diammonium phosphate, (NH HPO The finished detwisted yarn was of the same quality as that of Example 1.

EXAMPLE HI I A black pigment additive dispersion was made up from two components, one of which is Black VS, and 11.5% by weight dispersion of carbon black in water, and the other a 20% by Weight dispersion of Dianisidine Blue in water. These two dispersions were injected into a viscose solution at a point behind the spinning jet, the formulation being 32.6% by weight of the Black VS dispersion to 3% by Weight of the Dianisidine Blue dispersion based on the Weight of the cellulose in the viscose. The viscose solution contained 7.6% cellulose, 6.4% sodium hydroxide and 37% CS by weight and had a salt test of 4.7. The blended pigmented viscose was spun through a 60 hole jet at 60 m./m., into a spinning bath comprising an aqueous solution of 9% sulfuric acid, 2% zinc sulfate and 16% sodium sulfate, the bath temperature being 46 C. After a 14 inch immersion in the bath the resulting filaments were withdrawn as a yarn, box spun, and cake processed by the following steps: washed acid free, treated with a desulfiding solution comprising a weak solution of sodium sulfide and sodium carbonate, and then treated successively with a water rinse, a bleach, an acid, an antichlor (sodium thiosulfate), and a water wash.

The yarn was then treated in the manner of Example I, i.e., twisted, impregnated with hot formaldehyde in the presence of a curing catalyst, cured, and detwisted. A

portion of the detwisted yarn was then compared with another portion of the same yarn in skein form, i.e., treated the same except never twisted. In addition both samples were compared with a Swiss Viscose Helanca yarn made by supertwisting a 400-denier bright rayon yarn, then treating it with a urea-formaldehyde resin, curing, and detwisting. The properties tested were tensile strength and extensibility. Results are set forth in Table I.

The dry extensibility is a measure of the stress-strain relationship at the break point and here the higher the figure the better. However, in the case of wet extensibility a higher value is undesirable because it means that the yarn will stretch excessively under tension when wet. It is evident that on this point both colorspun samples are superior to the Helanca. The superior tensile strength of the colorspun samples is even greater than indicated when one considers that these two yarns are of smaller denier than the Helanca.

A Swiss Viscose Helanca yarn was compared with the yarn spun by the process of Example III to give an indication of the fixed formaldehyde content of the latter. Each sample was treated twice, with the results shown in Table II.

The fixed formaldehyde content is an index of the amount of cross-linking in the fiber. The superiority of the colorspun yarn in this regard is especially surprising in view of the fact that Helanca is resin-coated and hence is amenable to three-way cross-linking between the resin, the formaldehyde, and the cellulose whereas colorspun yarn has only the two-way cross-linkage between the formaldehyde and the cellulose. I

The box-spun yarn from Example III did not give a water-resistant bulky yarn when treated in the order of: soaking 18 minutes in skein form at 84 C., drying, twisting 45 t.p.i., curing 35 minutes at C., and detwisting. Although bulky as formed, it flattens out in water like regular rayon.

To determine the wet-swelling characteristics of colorspun bulky yarn of this invention three samples of this yarn were compared with an untreated colorspun yarn of the same type and a conventional box spun rayon. The percent swelling is the ratio of the diameter of the dry fiber to that of the wet fiber. Results are given in Table III below:

Since the swelling is based on the water absorption of the fiber it is evident that samples 1 and 2 above are superior to both conventional colorspun and plain rayon in this respect and that their dimensional stability and laundry resistance is better accordingly.

The useful cross-linking catalysts may be described as water-soluble weak acids and acid salts which, in concentrations of 0.25 to 0.50% by weight in water, form aqueous solutions having an acidic pH or which, on heating, dissociate to evolve a volatile base, leaving an acidic residue. Examples of preferred catalysts are monobasic and diabasic ammonium phosphates. Other operative catalysts are oxalic, tartaric, lactic, citric, formic, propionic, boric, and succinic acids, ZnCl NH4C1, and a mixture of Na SO and NaHSO A preferred catalyst is heterogeneous reaction product of 0.9 mole mend ethanolamine, 1.0 mole HCl, and 2.0 moles CH O. The reaction is favored by a pH of 3.5-2.9 in the treating bath. At this pH range the reaction time should be .15-25 minutes, preferably about 20, and the temperature should be 84 C. :2. Raising the temperature of the bath is desirable in many respects. It penetrates better and gives uniform treatment as well as increasing the rate of reaction, i.e., cross-linking. Temperatures higher than about 84 C. at the preferred pH range of the bath are not desirable due to their deteriorating effect on the yarns. Of course the higher the temperature the shorter should be the time of exposure to the formaldehyde.

Since the pH variation is an important factor, overdrying should be avoided by drying at a low temperature rather than a high temperature. If high temperature drying is to be used, humidity of air must be controlled. Any change of drying condition must be compensated for during curing. Thus, the more severe the drying conditions the less cure is required.

The degree of twist is inversely proportional to the denier of the yarn. For example in twisting a 300 denier filament 45 t.p.i. is a practical value. At 150 denier the t.p.i. could go up to 55. At 400 denier the t.p.i. would be 35-40.

All the samples in Examples I-III were in the form of spools under tension which is desirable when impregnation or when heat setting takes place. An aluminum spool with perforated wooden core was used to wind 300 yards at the maximum. Perforated metal pipe (e.g. Hastelloy) is ideal in treating larger quantities.

While the incorporation of the pigment into a continuous filament yarn followed by twisting, cross-linking, etc. is of practical value in reducing wet-swelling (a function of water-retention) and wet extensibility, the process is of even greater value with staple fibers. Dimensional stability is a much more serious problem in staple than in continuous filament and hence the resinification process has high potential for viscose staple. The incorporation of pigments into crimp type staple followed by the curing condensation reaction results in crimp fixation. Crimp set staple fiber produces spun yarns exhibiting bulk since the crimp resists deformation and fiber packing during the yarn spinning processes. This leaves voids in the resin-containing yarn which are absent in the ordinary staple yarn and thereby increases its volume per unit weight accordingly. Furthermore the improved cross-linking action on the filament improves its crush resistance in pile fabrics both in the form of continuous filament and staple. In addition, it increases the crease resistance of flat fabrics and the fabric is less Water sensitive and therefore faster drying.

It will be apparent from the foregoing that the invention provides a new method of improving the crimp or bulk and reliably decreasing and controlling the water retention and wet extensibility of regenerated cellulose yarns and textiles.

I claim:

1. A process for producing a bulky yarn from a pigmental cellulosic yarn comprising supertwisting the pigmented yarn, setting the twist therein by impregnating the twisted yarn with formaldehyde at an elevated temperature and in the presence of an acidic catalyst, thermally curing the impregnated yarn, and then detwisting the cellulosic yarn to produce a wool efiect which is substantially fast to washing.

2. Process of claim 1 wherein the catalyst is an amnionium phosphate.

3. Process of claim 1 wherein the catalyst is a heterogeneous reaction product of monoethanolamine, HCl, and formaldehyde.

4. Process of claim 3 wherein the reaction product is formed from about 0.9 mole monoethanolamine, about 1.0 mole HCl, and about 2.0 moles formaldehyde.

5. Process of claim 1 wherein the impregnation temperature is -90" C. and the curing temperature is at least C.

6. A process for producing a bulky yarn from a pigmented cellulosic yarn comprising supertwisting a pigmented yarn of -400 denier to a twist of about 55-40 turns per inch, impregnating the twisted yarn with a formaldehyde solution containing 0.25-0.3% of an acidic catalyst, said solution having a temperature of about 83 C.86 C., centrifuging, drying at an elevated temperature, curing for a time of 10-40 minutes at a temperature of 100175 C., and then detwisting to zero to produce a crimped yarn.

References Cited in the file of this patent UNITED STATES PATENTS 2,019,185 Kagi Oct. 29, 1935 2,516,562 Graham July 25, 1950 2,777,277 Lyon Jan. 15, 1957 FOREIGN PATENTS 534,698 Great Britain Mar. 14, 1941 

1. A PROCESS FOR PRODUCING A BULKY YARN FROM A PIGMETAL CELLULOSIC YARN COMPRISING SUPERTWISTING THE PIGMENTED YARN, SETTING THE TWIST THEREIN BY IMPREGNATING THE TWISTED YARN WITH FORMALDEHYDE AT AN ELEVATED TEMPERATURE AND THE PRESENCE OF AN ACIDIC CATALYST, THERMALLY CURRING THE IMPREGNATED YARN, AND THEN DETWISTING THE CELLULOSIC YARN TO PRODUCE A WOOL EFFECT WHICH IS SUBSTANTIALLY FAST TO WASHING. 